Spinal metastases are a common manifestation of many types of cancer. Specifically, metastatic lesions in the spine have been found in 90.5%, 74.3% and 45% of patients who died from prostate, breast and lung cancer, respectively. Additionally, approximately 200,000 patients die with metastatic lesions in their spine each year in the United States alone. Vertebral metastases cause pain, can degrade bone strength, and, due to the proximity of the spinal cord, can lead to serious neurological complications resulting from vertebral collapse. Treatment must address the tumor itself as well as the structural deficiency it may cause in the bone. The conventional treatment often occurs in two steps—a surgical procedure in which polymethylmethacrylate (PMMA) bone cement is injected into the vertebral body to restore strength to the bone (vertebroplasty or kyphoplasty), followed by multiple daily radiotherapy sessions to control tumor growth. The most common type of radiotherapy for spinal metastases is external beam radiation therapy (EBRT). Although EBRT effectively delivers radiation to the vertebral body, adjacent radiosensitive tissues such as the spinal cord and nerves are also irradiated, often limiting the dose that can be safely delivered to the tumor. Thus, to maximize treatment effectiveness while minimizing collateral damage to normal tissue, EBRT is fractionated into ten daily treatment sessions, inconveniencing patients whose quality of life has already been compromised. Intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT) have emerged as improved radiotherapy techniques, but both techniques still require multiple treatment sessions, still irradiate the spinal cord and nerves (albeit to a lesser extent), and are expensive.
The use of vertebroplasty and kyphoplasty is likely to increase, as both procedures can provide immediate pain relief and patients with metastatic bone disease are living longer. However, conventional radiation therapy modalities can be inconvenient for the patient, as they are performed separately from the surgical procedure and are usually fractionated into multiple treatment sessions to minimize the collateral damage to normal tissue that occurs when radiation is delivered using an external irradiation source. Although radiotherapy can be given in fewer fractions with similar pain relief, patients treated with a single fraction tend to require retreatment more often than patients treated with multiple fractions.